The objective of this project is to characterize dose-response relationships and toxicity of gallium oxide administered by inhalation to rats and mice in 14-day repeated-dose and 90-day subchronic studies. Animals will be exposed for 6 hours per day, 5 days per week for 14 and 90 days. At the end of each study, all animals will be given gross and microscopic histopathologic evaluations. Hematology, clinical chemistry, urinalysis, and sperm morphology/vaginal cytology will be performed in the 90-day study. The results of each study will be used by NTP to establish exposure concentrations to be used in the next study (i.e., the 14-day results for the 90-day study; the 90-day results for a possible chronic study.